In recent years, high-speed printing such as direct mail printing has been performed using inkjet image recording apparatuses. With such image recording apparatuses, an individual piece of information (so-called variable information) is recorded on a region of a recording sheet, which is roll paper, corresponding to each page. In images recorded by the inkjet image recording apparatuses (hereinafter, referred to as “recorded images”), dot missing may occur due to nozzle clogging caused by adherence of dirt, clusters of dots, or the like. Accordingly, an inspection apparatus for detecting such a defect is installed in the image recording apparatuses.
In the case of defect inspection of a recorded material on which the same image has been repeatedly recorded, the defect inspection is performed such that a sample image is prepared by capturing a recorded image that does not include a defect, and an image obtained by capturing a recorded image of an object to be inspected (hereinafter, referred to as an “inspection image”) is compared with the sample image. Acquiring the sample image and the inspection image with a common camera makes it possible to eliminate negative influences such as recording unevenness and variations in light quantity and to obtain the same brightness and resolution, thus enabling the defect inspection to be relatively easily performed. However, in the case where variable information is recorded, a sample image cannot be prepared, and the need arises to compare an inspection image directly with (data of) an original image used in recording. In this case, defect inspection becomes difficult because the original image and the inspection image have different levels of resolution and brightness.
In relation to the defect inspection of a recorded material that includes variable information, with the apparatus for inspecting an ink jet printing part disclosed in Japanese Patent Application Laid-Open No. 2003-94627, inspection target X-axis projection data is generated by integrating pixel values in a predetermined direction in a variable data target image that is an image to be inspected. Furthermore, inspection reference X-axis projection data is generated by integrating pixel values in the same direction in a variable data part-inspection reference image serving as a reference image. In the inspection target X-axis projection data, a positional shift and a magnification error are corrected with respect to the inspection reference X-axis projection data and binarization is performed using a threshold value that approximates 0, as a result of which inspection target zero extraction data is generated. In the inspection reference X-axis projection data as well, positions with a value of 0 are extracted so as to generate inspection reference zero extraction data. Then, zero portions that are common to those in the inspection reference zero extraction data are removed from the inspection target zero extraction data, and as a result, dot missing data is generated. With the apparatus for inspecting an ink jet printing part, dot missing is detected based on the dot missing data.
With the inkjet printer disclosed in Japanese Patent Application Laid-Open No. 10-100412, an identification pattern is printed between a plurality of print images on rotary press paper, and a print problem with the print images is checked by checking the presence or absence of ink drips and dot missing in the identification pattern.
Incidentally, with the method disclosed in Japanese Patent Application Laid-Open No. 2003-94627, in the case of color images, even if dots of one color ink are missing in a color mixed portion, the value obtained by integrating pixel values in that portion does not always increase because of the presence of other color inks, and there are cases in which dot missing cannot be detected. Also, in a portion that has low ink density, even if there is no dot missing, the value obtained by integrating pixel values in the inspection image can easily increase due to the influence of ink landing accuracy, and there is the risk of erroneously detecting a defect. Furthermore, with the inkjet system, even during normal recording, variations can occur due to, for example, individual differences in recording sheet and nozzles. Thus, a threshold value for integrated values, which is used in determining the presence of dot missing, cannot easily be determined.
In the inkjet image recording apparatuses, dot missing appears or disappears in the middle of recording. Thus, even if the presence or absence of defects on the identification pattern is checked as disclosed in Patent Application Laid-Open No. 10-100412, it is difficult to appropriately determine the presence or absence of defects in print images. Furthermore, because it is necessary to print an identification pattern of the same width as print images in the width direction of the rotary press paper, a space for recording an identification pattern is required on top and bottom sides of each page. However, for example, in the case where a pattern is recorded across the perforation between pages on a recording sheet, a space for printing an identification pattern cannot be retained.